Resilient behavior of bio-cemented sandy soil treated with enzyme-induced carbonate precipitation for pavement applications

Subgrade stability is a key factor that influences the long-term performance of the pavement structure under repeated traffic loading. Enzyme-induced carbonate precipitation (EICP) has been recently explored as a bio-inspired solution to improve the mechanical properties of sandy soils. This study evaluates the potential of EICP to cement silica sand as a treated subgrade in pavement applications. The study investigated the mechanical performance of EICP-treated sand compacted at varying initial degrees of saturation and treatment cycles through repeated loading triaxial (RLT) and unconfined compressive strength (UCS). The results show that specimens having a lower initial EICP degree of saturation facilitated efficient carbonate precipitation bridging between sand grains, resulting in higher resilient modulus and UCS. Furthermore, surface percolation of EICP cementing solution resulted in a further increase in carbonate content and treated soil UCS and resilient modulus (M_r). A maximum UCS and M_r values of about 700 kPa and 165 MPa, respectively, were achieved, which implies the possibility of using EICP-treated sand as a treated subgrade layer or subbase to reduce the base layer thickness or improve the pavement structure performance. The Scanning electron microscopy (SEM) images further explained the influence of the carbonate crystal shape and morphology on the treated soil strength and modulus. Finally, simulations executed using AASHTOWare Pavement ME Design software show the potential of utilizing EICP for improving subgrade for pavement structures, with a significant reduction in base layer thickness while maintaining the same rutting and fatigue performance. Hence, demonstrating the potential of EICP in enhancing subgrade properties for pavement structures.